In order to monitor a device, transducers may be mounted to the device, which may for example be an engine, in particular a gas turbine engine. The transducer may sense acoustic stress waves, stress waves, vibration magnitudes and/or frequencies, temperatures, pressures, chemical compositions or any other environmental factors. As such, the transducers may assist in the development, monitoring or maintenance of the engine.
Acoustic stress waves, also referred to as “stress waves” or “acoustic emissions”, are transient elastic waves within a material caused by the release of localised stress energy. The stress energy may be released by events such as cracking or rubbing of the microstructure of the material, and may occur before structural damage is visible.
FIGS. 1a and 1b show a transducer 2 mounted to a waveguide 4 which is in turn connected to a flange portion 6 of an engine. The shape of the waveguide 4 may be defined by the need to remove the transducer 2 from the immediate vicinity of the engine due to operating temperature limitations. The transducers may be mounted by bolting the waveguide 4 to the external flange portion 6. This requires the removal of a potentially critical casing bolt 8 that must then be properly reassembled with the waveguide 4 in place. The transducer 2 is typically coupled to the waveguide 4 simply by wrapping insulating tape around the transducer and waveguide. In the example shown, the transducer 2 converts energy from acoustic stress waves into an electrical signal and the signal is transmitted via an electrical cable 10.
There are, however, two main disadvantages with the current mounting system:
Firstly, the removal of the critical engine casing bolts in order to attach the waveguide is undesirable. Typically, this limitation has restricted testing to development engines only, particularly in the field of gas turbine engines. Developments in Engine Health Monitoring has advanced to the point where large amounts of actual engine data is required for analysis. The most effective way of obtaining this data is to test on production engines during pass-off testing due to the much higher rate at which they are tested. The removal of critical casing bolts is not desirable in this application as it may compromise the integrity of the engine.
Secondly, the use of insulation tape to connect the transducer to the waveguide is undesirable as it cannot provide a repeatable minimum contact pressure of the transducer with the waveguide.
The present invention therefore seeks to address these issues.